Conventionally, there has been known an electronic control unit having an electronic circuit board, a case for housing electronic components mounted on the electronic circuit board, and a cover. In such an electronic control unit, as a configuration of sealing between the cover and the case, for example, a seal groove is formed on a tip edge of a peripheral wall of the case, and is filled with a sealing material. Further, the cover has a protrusion, and the protrusion is inserted into the seal groove.